A combination lock with three dials, each numbered 1 through 8, is defective in that you only need to get two of the numbers right to open the lock. (For example, suppose the true combination is 4-2-7. Then 4-2-7 would open the lock, but so would 4-2-5, 4-2-2, 8-2-7, or 4-6-7. But not 2-4-7.)What is the minimum number of (three-number) combinations you need to try in order to be sure of opening the lock?